Radius of curvature at the talocrural joint surface: inference of subject-specific kinematics

The coupled behavior of talocrural joint motion is primarily determined by the morphological features of the talar trochlea and tibiofibular mortise. Features of the radius of curvature of the talocrural joint, however, remain unclear. The objectives of this study were to evaluate the radius of curvature at the mid, medial, and lateral regions of both the talar trochlea and the tibial plafond, and to estimate subject-specific kinematics of the talocrural joint.

Computed tomography images of 44 subjects with healthy talocrural joints were assessed by creating three-dimensional bone models. The radii of curvature of the anterior and posterior regions at the mid, medial, and lateral regions of both the talar trochlea and the tibial plafond were calculated. Hypothetical dorsiflexion and plantarflexion axes of the talocrural joint were estimated from the shape of the talar trochlea. Orientations and distances of these axes were calculated.

At both the talar trochlea and the tibial plafond, the anteromedial and posteromedial radii exhibited the largest coefficients of variation. The anterior-to-posterior radius ratio (APRR) of the medial talar trochlea significantly correlated with the mid APRR, anterior medial-to-lateral radius ratio (MLRR), and posterior MLRR of the trochlea (r = 0.45, 0.52, - 0.60, respectively, and all P < 0.01).

The asymmetric shape of the medial talar trochlea seems to determine a fixed or changing axis of rotation at the talocrural joint. This subject-specific rotational axis of the talocrural joint should be considered in the management of patients with ankle injuries.